In recent times, research and development on nucleic acid medicines, which contain nucleic acids as an active ingredient, has intensively been conducted. Plenty of researches have been conducted, for example, on nucleic acid medicines comprising nucleic acids such as siRNA, miRNA, miRNA mimic or antisense oligonucleotide, having a resolving action or function-suppressing action against a target mRNA. In addition, researches on nucleic acid medicines for expressing a target protein in cells have been conducted. In connection with these research and development, technologies for introducing nucleic acids with a high efficiency into cells, tissues or organs as drug delivery systems (DDS) technologies have been being developed.
As the above mentioned DDS technologies, a technology introducing nucleic acids into cells after mixing the nucleic acid and lipids to form a complex via said complex has traditionally been known. As lipids used for forming the above mentioned complex, cationic lipids, hydrophilic polymer lipids or helper lipids are traditionally known. As the above mentioned cationic lipids, compounds described in Patent Literature 1 to 5 are known.